Damaged heart valves are now often replaced with mechanical valves of the type described, for example, in U.S. Pat. No. 4,021,863. Mechanical valves are commonly provided with a generally circular base about which is provided a suturing ring. In the process of implanting a mechanical heart valve, the natural valve orifice is prepared by surgical removal of damaged or diseased valve tissue, leaving the orifice with an open, generally circular configuration. The mechanical valve of proper size is then appropriately affixed in the natural valve orifice by stitching the suturing ring to the surrounding valve orifice tissue. The sizes of natural heart valve orifices may vary considerably between patients, and the sizes of the valve orifices for the different valves of the heart may vary as well. For example, there are significant size differences even in a normal heart between mitral, aortic, tricuspid and pulmonary valve orifices. To avoid undue stresses on sutured heart valve orifices, and to provide optimum implant results, good practice suggests that the surgeon measure the orifice size with a measuring gauge, and then select an appropriately sized mechanical valve.
Measuring gauges of the type referred to above have been provided in a series of sizes, the gauges having cylindrical end portions of given diameters. The sizing operation involves selecting that particular gauge that exhibits the desired "fit" in a natural heart valve orifice. One such gauge comprises a handle having at its forward end a cup-shaped device, the flat, closed bottom of the cup facing forwardly away from the handle. This gauge, in modified form, includes a flange extending radially outwardly from the rearward open mouth of the cup-shaped device. Yet another gauge is provided with a finger-like projection having a smooth, bullet-shaped nose at its forward end and an outwardly diverging skirt at its rearward end, the projection being attached to a rearwardly extending handle.
Although positive results have been obtained using such gauges (often termed "obturators"), certain problems have arisen with the use of such devices. The gauges of the type described above interfere with and largely block the surgeon's view of the interior of heart chambers during the sizing operation, since such devices, even though made of transparent material, rapidly become obscured by blood. It should also be observed that additional surgical removal of annular heart tissue within or adjacent to an orifice is often necessary to permit the mechanical valve to be properly accomodated and to remain operable within the natural heart valve orifice. The sizing gauges referred to above, however, tend to indicate orifice size only, and do not permit the surgeon to view the inwardly visible external periphery of the natural heart valve orifice. Further, there is a risk that certain of the gauges, such as those employing the cup-shaped elements referred to above, may actually pass through an orifice to be sized and into a heart chamber on the other side of the orifice. The relatively sharp edges at the rearward portion of gauges of this type render their removal back through the valve orifice not only difficult to accomplish, but potentially traumatic to the annular heart tissue.
Insertion of such (prior art) sizing gauges within a heart orifice such as the aortic valve orifice may produce pressurization of the heart cavity beyond the valve. For example, when the sizing procedure is employed for the aortic valve from the aortic aspect, the left ventricle may become pressurized, the sizing gauge sliding through the valve orifice in much the same manner that a piston slides through a cylinder. When the surgeon encounters resistance to further insertion of the sizing gauge due to cavity pressurization, the resistance may erroneously be interpreted to a supposed contact of the sizing gauge with annular heart tissue and may result in inaccurate gauging of the tissue orifice and a consequent poor choice of mechanical valve size.
There is thus a clear need in the surgical field for a valve sizing gauge which would not obstruct the surgeon's view during the sizing operation. It is also desirable to provide a sizing gauge which, following inadvertent passage of the gauge through a heart orifice, could be easily retrieved through the orifice with a minimum of difficulty and trauma.